1. Field of the Invention
The invention relates to a method of measuring the degree of mis-match which would be obtained between first and second signals should their time-axes be subjected to a time alignment (if any) which is required to minimize the degree of mis-match, in which method the values of both signals are sampled at regular time intervals, the sampled values are stored, a difference value and a distance value is obtained for each combination of a sampled value of the first signal and a sampled value of the second signal, at least if the corresponding distance value is less than a predetermined amount. Said difference and distance values are obtained in succession for the combinations of the first sampled value of the first signal and the successive sampled values of the second signal, the next sampled value of the first signal and the successive sampled values of the second signal, and similarly up to the last sampled value of the first signal and the successive sampled values of the second signal. Each said distance value is determined from the corresponding difference value and the smallest of those three adjacent distance values (if present) which have been obtained for the combination of the corresponding sampled value of the first signal and the sampled value of the second signal immediately preceding the corresponding sampled value of the second signal, the combination of the corresponding sampled value of the second signal and the sampled value of the first signal immediately preceding the corresponding sampled value of the first signal, and the combination of the sampled values of both signals immediately preceding the corresponding sampled values of the first and second signals, and a measure of the said degree of mis-match is derived from the distance value obtained for the combination of the last sampled values of both signals.
The invention also relates to an apparatus for carrying out such a method.
2. Description of the Prior Art
Such a method, used for speech recognition purposes, is known from the magazine "IEEE TRANSACTIONS ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING", Vol. ASSP-26, No. 1, February 1978, pages 43 to 49.
In many cases each signal will comprise a plurality of components, as is the case with speech signals which can be divided into a plurality of spectral ranges by means of a filter bank. A plurality of distance values could be obtained for such signals by applying the method separately for each component. However, this may give rise to different relative shifts and/or distortions for the time-axes when the method is applied for the different components, which does not correspond to reality and which may yield incorrect or non-optimum measurements. This may be the case if the degree of mis-match between the sound level variation of a test speech signal and the corresponding variation of a plurality of reference signals corresponding to different words is measured, the reference signal with the best conformity is determined from the various residual differences obtained, and it is also required to recognize the characteristics which are typical of a particular speaker. It is an object of the invention to enable this problem to be overcome.